This disclosure is directed to a method for the manufacture of 2-hydrocarbyl-3,3-bis(hydroxyaryl)phthalimidines, particularly to the manufacture of N-phenyl phenolphthalein bisphenol and N-methyl phenolphthalein bisphenol. This disclosure is also directed to the manufacture of polycarbonates from the prepared 2-hydrocarbyl-3,3-bis(hydroxyaryl)phthalimidines.
2-Hydrocarbyl-3,3-bis(hydroxyaryl)phthalimidines such as N-phenyl phenolphthalein bisphenol (PPPBP) can be used in the manufacture of homopolycarbonates and copolycarbonates. Commercially, PPPBP is synthesized from aniline and phenolphthalein in the presence of hydrogen chloride. The staring material, phenolphthalein, can be manufactured from phthalic anhydride and phenol.
There are several challenges associated with the commercial process. For example, crude PPPBP obtained via this process typically contains aminophenol impurity, 2-aryl-3-(aminoaryl-3-(hydroxyaryl)phthalimidine, which must be removed through several activated carbon treatments. Final purification is conducted by a trituration using a methanol/water solvent system to bring the phenolphthalein within specification limits and to improve the color of the monomer. This multistep purification process uses large amount of activated carbon which is recycled only for few cycles and hence generates waste. In addition, the multistep purification process involves multiple unit operations which lead to yield losses.
Accordingly, it would be desirable to develop a process for the preparation of 2-hydrocarbyl-3,3-bis(hydroxyaryl)phthalimidine that reduces or avoids formation of aminophenol impurity and waste generation, for example by avoiding the use of activated carbon. It would also be desirable if this process provides 2-hydrocarbyl-3,3-bis(hydroxyaryl)phthalimidine of high yield and purity.